Why are my tool menus tiny? (pic)
It seems you have high-dpi screen. If this is the case, see here: Make Blender usable on high resolution screen.

In a nutshell, go to Preferences -> System -> DPI. Play around with the value until you are comfortable. If that isn't enough, see the link.

To actually answer your question: they are tiny, because they are fixed to a pixel size and your pixels are tiny.